It is the principal objective of the proposed research to elucidate the metabolism and function of phospholipids, essential building blocks of biological membranes throughout nature. The synthesis of phosphatidylcholine, sphingomyelin and phosphatidylethanolamine will be intensively investigated in animal tissues, particularly liver and lung. The biogenesis of membrane lipids, and the origin of lipid asymmetry in the membranes of E. coli and B. megaterium will also be studied. Another major aspect of the proposed program is the regulation of the synthesis of membrane lipids in animal tissues and in bacteria.